Proteinase inhibitor I27, calpastatin (IPR001259)

Short name:
Prot_inh_calpain

Description

This entry represents repeats on calpain inhibitor proteins.

Calpain inhibitor (calpastatin) is restricted to the metazoa and specifically inhibits calpain (calcium-dependent cysteine protease) [PMID: 15255177]. Calpastatin belongs to MEROPS inhibitor family I27, clan II. It plays a key role in post-mortem tenderisation of meat and may be involved in muscle protein degradation in living tissue.

The calpain system originally comprised three molecules: two Ca2+-dependent proteases, mu-calpain and m-calpain, and a third polypeptide, calpastatin, whose only known function is to inhibit the two calpains. Both mu- and m-calpain are heterodimers containing an identical 28kDa subunit and an 80kDa subunit that shares 55-65% sequence homology between the two proteases. The single calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17kDa to 85kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent.

How calpain activity is regulated in cells is still unclear, but the calpains
ostensibly participate in a variety of cellular processes including remodelling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma [PMID: 12843408].